This invention relates to hydraulic systems for controlling a plurality of actuators such as hydraulic cylinders which are found, for example, in earth moving equipment such as excavators and cranes. In such a system, it is conventional to provide a pilot operated control valve for each actuator which is controlled by a manually operated controller through a pilot hydraulic circuit. The control valve functions to supply hydraulic fluid to the actuator to control the speed and direction of operation of the actuator. In addition, the control valve for each actuator controls the flow of hydraulic fluid out of the actuator. It is also common to provide counterbalance valves or fixed restrictions to control overrunning loads.
In the copending U.S. application of Robert H. Breeden et al, Ser. No. 024,058, filed Mar. 26, 1979, now U.S. Pat. No. 4,201,052, having a common assignee with the present application, there is disclosed and claimed a hydraulic system for accurately controlling the position and speed of operation of the actuators; which system is simple and easy to make and maintain; which system is unaffected by change of load pressure of various portions of the system or other actuators served by the same source; which system may not use flow from the pressure source in the case of overrunning loads on the actuators; wherein the control valves may be mounted adjacent the actuator for preventing loss of control of the load in case of malfunction in the hydraulic lines to the actuator; wherein the valves which control flow out of the actuator function to control the velocity in the case of energy generating loads, wherein the valve that controls flow into the actuator controls the velocity in the case of energy absorbing loads; wherein the valve system for each actuator can be mounted on its respective actuator and incorporates means for preventing uncontrolled lowering of the load in case of pressure failure due to breaking of the lines to the valve system; wherein the timing of operation of the valve controlling flow into the actuator and out of the actuator can be designed to accommodate the specific nature of the particular load.
It is an object of the present invention to provide a dual acting hydraulic control system having dual meter-in valves for controlling dual-acting hydraulic actuators.
Another object of the present invention is to provide a dual acting hydraulic control system having dual meter-in valves for providing control of dual-acting hydraulic actuators in a regenerative mode.
A further object of the present invention is to provide a single acting hydraulic control system for controlling single acting hydraulic actuators.
The present invention comprises a hydraulic control system for use with a hydraulic actuator, a pilot controller, and a pump. The actuator includes a movable element and a pair of openings adapted to function alternately as inlets or outlets for moving the element in opposite directions. The pilot controller supplies fluid to the system at pilot pressure and the pump supplies fluid at pump pressure to the actuator. The control system includes a line adapted for connection to each of the openings and a meter-out valve associated with each of the lines for controlling fluid flow from the actuator. The meter-out valves are each selectively pilot operated by pilot pressure from the pilot controller. A meter-in valve is positioned in each of the lines for controlling fluid flow from the pump to the actuator with each of the meter-in valves being selectively operable by pilot pressure from the pilot controller.
In one embodiment of the present invention the actuator includes a head end and a rod end associated with each of the pair of openings and each of the lines adapted to be connected therewith having a load drop check valve associated with the head end and rod end, respectively. A means for venting the load drop check valve associated with the rod end and means for simultaneously opening the meter-in valves provide control of fluid flow to the actuator in a regenerative mode.
Another embodiment of the invention comprises a hydraulic control system for use with a hydraulic actuator having a movable element and an opening adapted to function alternately as an outlet and an inlet for moving the element. A pilot controller controls a supply of fluid at pilot pressure and a pump supplies fluid at pump pressure to the actuator. The hydraulic control system comprising a single line adapted for connection to the opening of the actuator and a single meter-out valve associated with the line for controlling flow from the opening. The meter-out valve being pilot operated by pilot pressure from the pilot controller. A single meter-in valve is positioned in the line for controlling fluid flow from the pump to the actuator with the meter-in valve being operable by pilot pressure from the pilot controller.
These and other objects, advantages, and details of the invention may be had from the following drawings and description taken together with the accompanying claims.